Orbits, stabilizers and their index
For a left action, Orb(x)={g·x:g∈G} and Stab(x)={g:g·x=x}.
Key knowledge
For a left action, Orb(x)={g·x:g∈G} and Stab(x)={g:g·x=x}. Orbits partition X and Stab(x) is a subgroup. For finite G,X the map g Stab(x)↦g·x bijects left cosets with Orb(x), so |Orb(x)|=[G:Stab(x)]=|G|/|Stab(x)|.
Conditions and scope
- Fix one specified action and a point x∈X.
- A fixed-point set lies in X; a stabilizer lies in G.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Proposition 13.6/13.10, Remark 13.8 and Theorem 13.11 including inverse-closure and coset-map proof.
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Entry details
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- math-orbit-stabilizer
- Revision
- university-core.1
- Structured reference record
- University core expansion